Display devices used while being worn on human bodies, such as display devices mounted on heads, have recently been developed and are referred to as head-mounted displays or wearable displays. It is desired that not only display devices but also electronic devices used while being worn on human bodies (such electronic devices are also referred to as wearable devices), such as hearing aids, have a light weight and a small size.
Most wearable devices and portable information terminals include secondary batteries that can be repeatedly charged and discharged, and have problems in that there is a limitation on the time for operation of the wearable devices and the portable information terminals because of their light weight and compactness. Secondary batteries used in wearable devices and portable information terminals should be lightweight and compact and should be able to be used for a long time.
Along with a decrease in weight of electronic devices, it is demanded that secondary batteries for supplying power to electronic devices also have a light weight and a small size.
Electronic book readers including flexible display devices are disclosed in Patent Documents 1 and 2.